Starting and operating circuit for gas discharge lamp

Abstract

Starting and operating power is provided to a gas discharge lamp by a circuit which includes a constant-voltage current-limiting ferroresonant transformer connected to an AC source and having high and low voltage output terminals. A full-wave rectifying bridge is selectively connectable to either the high or low voltage output terminals by relay control means which includes a choke coil connected in series with the lamp and a magnet reed. On starting of the lamp the magnetic flux of the choke coil operates the reed for shifting to the low voltage condition, and on extinguishing of the lamp the collapse of the choke coil flux operates the reed for shifting to the normal high voltage condition. A transient high voltage starting pulse is applied to the lamp across a spark gap by a pulse generating starting circuit in which a capacitor, charged from the DC output, is discharged through a self-commutating SCR and an ignition transformer. The transient pulse is effectively blocked from the DC supply by the choke coil and two diodes. Capacitive discharge means is also provided for maintaining operating voltage to the lamp during the switching of the power supply. For higher power applications there is provided an alternative AC supply circuit utilizing two constant-voltage current-limiting ferroresonant transformers, the control means switching the transformers between series and parallel connection for high and low voltage output, respectively.

What is claimed is: 
     
       1. A circuit for starting and operating a gas discharge lamp comprising means connecting the lamp to an associated source of DC voltage, a starting circuit for producing a transient pulse of starting voltage sufficiently high to ignite the lamp when it is warm, and spark gap means connected to said starting circuit and connected directly to the lamp for coupling said transient starting voltage pulse to the lamp to start same while preventing feedback of the DC voltage to said starting circuit. 
     
     
       2. The circuit of claim 1, wherein said means connecting the lamp to the associated source of DC voltage includes means preventing feedback of said transient voltage pulse to the DC source. 
     
     
       3. The circuit of claim 1, wherein said starting circuit includes a storage capacitor connected to the source of DC voltage for charging thereby, autotransformer means connected to said spark gap means, and discharge means connected between said capacitor and said autotransformer and responsive to a predetermined voltage across said capacitor for discharging same through said autotransformer to produce said transient voltage pulse. 
     
     
       4. The circuit of claim 3, wherein said discharge means includes a silicon controlled rectifier having an anode connected to said capacitor and a cathode connected to said autotransformer and a gate electrode, and a resistor and a diac connected in series between said anode and said gate electrode for triggering said silicon controlled rectifier to a conductive state when the voltage on said capacitor reaches said predetermined voltage. 
     
     
       5. A circuit for starting and operating a gas discharge lamp comprising power supply means connected to the lamp and shiftable between a normal starting condition for applying a relatively high DV voltage to the lamp and a running condition for applying a relatively low DC voltage to the lamp; said power supply means including a constant-voltage transformer having primary winding means adapted for connection to an associated source of AC voltage and secondary winding means having first and second and third terminals, and rectifying means selectively connectable between said first and second terminals in said running condition or between said first and third terminals in said starting condition; control means coupled to said power supply means and to the lamp and operative for shifting said power supply means to the running condition thereof in response to starting of the lamp and for shifting said power supply means to the starting condition thereof in response to extinguishing of the lamp; and starting means coupled to said power supply means and to the lamp and responsive only to the relatively high DC voltage when said power supply means is in the starting condition thereof for producing a transient pulse of starting voltage and applying it to the lamp for starting thereof. 
     
     
       6. The circuit of claim 5, wherein said power supply means in the starting condition thereof provides a voltage of approximately 400 VDC and in the running condition thereof provides a voltage of approximately 150 VDC. 
     
     
       7. The circuit of claim 5, and further including energy storage means connected to said power supply means and to the lamp and responsive to shifting of said lamp from said starting condition to said running condition thereof for supplying current to the lamp to maintain the lamp lighted during the shifting of said power supply means. 
     
     
       8. The circuit of claim 5, wherein said transformer is a ferroresonant, current-limiting transformer. 
     
     
       9. A circuit for starting and operating a gas discharge lamp comprising power supply means connected to the lamp and shiftable between a normal starting condition for applying a relatively high DC voltage to the lamp and a running condition for applying a relatively low DC voltage to the lamp, first control means coupled to said power supply means and operable in first and second conditions respectively for shifting said power supply means to the starting and running conditions thereof, second control means coupled to said first control means and connected in series with the lamp and responsive to the lamp current for shifting said first control means to the second condition thereof in response to starting of the lamp and for shifting said first control means to the first condition thereof in response to extinguishing of the lamp, and starting means coupled to said power supply means and to the lamp and responsive only to the relatively high DC voltage when said power supply means is in the starting condition thereof for producing a transient pulse of starting voltage and applying it to the lamp for starting thereof. 
     
     
       10. The circuit of claim 9, wherein each of said first and second control means includes a relay. 
     
     
       11. The circuit of claim 10, wherein said second control means includes a choke coil connected in series with the lamp for isolating said power supply means from the transient voltage pulse applied to the lamp, said choke coil being responsive to lamp current for producing a magnetic flux, and relay means responsive to said magnetic flux for controlling said first control means. 
     
     
       12. The circuit of claim 9, wherein said power supply means includes a transformer having primary winding means connected to an associated source of AC power and secondary winding means having first and second and third terminals, and rectifying means selectively connectable between said first and second terminals in said running condition or between said first and third terminals in said starting condition, said first control means comprising a relay having a coil connected across said primary winding and a movable contact movable between said second and third terminals of said secondary winding means, said second control means including relay means having contacts connected in series with said first relay coil and a coil connected in series with the lamp. 
     
     
       13. A circuit for starting and operating a gas discharge lamp comprising power supply means connected to the lamp and shiftable between a normal starting condition for applying a relatively high DC voltage to the lamp and a running condition for applying a relatively low DC voltage to the lamp, control means coupled to said power supply means and to the lamp and operative for shifting said power supply means to the running condition thereof in response to starting of the lamp and for shifting said power supply means to the starting condition thereof in response to extinguishing of the lamp, a starting circuit coupled to said power supply means and responsive only to the relatively high voltage when said power supply means is in the starting condition thereof for producing a transient pulse of starting voltage sufficiently high to ignite the lamp when it is warm, and spark gap means connected to said starting circuit and connected directly to the lamp for coupling said transient voltage pulse to the lamp to start same while preventing feedback of the DC voltage to said starting circuit. 
     
     
       14. The circuit of claim 13, wherein said power supply means includes a ferroresonant constant-voltage current-limiting transformer, said circuit having an efficiency of approximately 80% and substantially unity power factor. 
     
     
       15. A circuit for starting and operating a gas discharge lamp comprising power supply means connected to the lamp and shiftable between a normal starting condition for applying a relatively high DC voltage to the lamp and a running condition for applying a relatively low DC voltage to the lamp; said supply means including two constant-voltage transformers each having primary winding means adapted for connection in series across an associated source of AC voltage and secondary winding means, rectifying means having input terminals, and switching means coupled to said secondary winding means and to the input terminals of said rectifying means and switchable between a first condition connecting said secondary winding means in series across said input terminals of said rectifying means in the starting condition of said power supply means and a second condition for connecting said secondary winding means in parallel across the input terminals of said rectifying means in the running condition of said power supply means; control means coupled to said power supply means and to the lamp and operative for shifting said power supply means to the running condition thereof in response to starting of the lamp and for shifting said power supply means to the starting condition thereof in response to extinguishing of the lamp; and starting means coupled to said power supply means and to the lamp and responsive only to the relatively high DC voltage when said power supply means is in the starting condition thereof for producing a transient pulse of starting voltage and applying it to the lamp for starting thereof.